The invention relates to an electrochemical cell comprising at least one electrode consisting of a substrate made of porous metal which is impregnated with an electrochemically active material.
The invention also relates to a method of producing such an electrochemical cell.
Examples of the use of electrochemical cells comprising such an electrode are fuel cells and sealed rechargeable cells.
U.S. Pat. No. 4,217,939 discloses an electrode made of a porous metal (foam metal or sponge metal) having interlinked pores, which are filled with an electrochemically active material in paste form. The electrode which is made of foam nickel filled with a nickel hydroxide-containing paste is suitable for use as the positive electrode in a rechargeable cell. The electrode is uniformly impregnated with the active material, the paste being provided, for example, at one side of the foam metal and is thereafter pressed therethrough. The porous metal is entirely filled with electrochemically active material and there is no free metal at the surface.
In several types of electrochemical cells reactions occur at the interface of a solid electrode, a liquid electrolyte and a gas present. That is, for example, the case not only in several types of fuel cells, but also in sealed rechargeable cells. In a gas-tight rechargeable nickel-cadmium cell or nickel-metal hydride cell oxygen recombination occurs at the negative electrode during excessive charging of the cell. In a nickel-metal hydride cell hydrogen recombination occurs at the positive electrode during excessive discharging of the cell. It is desirable for these reactions to proceed as rapidly as possible, for a fuel cell, because of the cell efficiency and for rechargeable cells because of their operating life, expressed in charging and discharging cycles. When in a rechargeable cell the recombination rate on charging or discharging is insufficient, the pressure in the cell increases. This may cause gas (possibly with electrolyte) to escape via a safety valve, which reduces the operating life and the capacity of the cell.